The present disclosure concerns an aerofoil, particularly but not exclusively, an aerofoil for a gas turbine engine having a reduced broadband noise profile in use.
Noise from aircraft is an ongoing environmental concern. There are typically several sources of noise from an aircraft, including jet noise produced by shear interaction between the jet exhaust from gas turbine engines, and aerodynamic noise caused primarily by turbulent air created by the flow of air over aircraft surfaces. One particular source of noise is due to interaction between a wake resulting from an upstream component such as a fan or propeller rotor impinging on the leading edge of a downstream component such as an Outlet Guide Vane (OGV).
As aircraft engine bypass ratios are increased, aircraft aerodynamic noise is becoming a relatively large contributor to overall aircraft noise. In particular, turbulence created on the leading and trailing edges of aerofoil surfaces is thought to produce a significant proportion of noise produced by an aircraft. Noise created by these mechanisms often has a wide range of frequencies (known as “broadband noise”), and is particularly difficult to eliminate.
Examples of aerofoils on aircraft include the wings and tail surfaces, as well as smaller components such as control surfaces and high lift devices such as flaps and slats. The gas turbine engines of the aircraft also typically include several aerofoils, including compressor and turbine rotors and stators, fan rotors and Outlet Guide Vanes (OGV). The gas turbine engine nacelle is also typically aerofoil shaped.
It has been proposed to provide wave-like projections on the leading edge of an aerofoil, as proposed for example in U.S. Pat. No. 6,431,498. It is thought that such projections reduce drag as well as reduce noise to some extent, as evidenced for example in US2013164488. Such projections have been proposed for both fixed and rotating aerofoils, as proposed for example in US2011058955.
However, such projections do not eliminate noise completely, and it is therefore desirable to provide an aerofoil having improved noise attenuation properties. Furthermore, these profiles may be relatively time consuming and expensive to produce, and may have relatively poor aerodynamic performance (i.e. high drag).
The term “chord” will be understood to refer to the distance between the leading and trailing edge of an aerofoil, measured parallel to the normal in use airflow over the wing. The term “chordwise” will be understood to refer to a direction parallel to the chord. The term “span” will be understood to refer to a direction generally normal to the chord, extending between a root and a tip of an aerofoil component. The term “spanwise” will be understood to refer to a direction parallel to the span.